1. Field of the Invention
The present invention relates to an enhanced surface-emitting photonic device and, more particularly, to an enhanced surface-emitting photonic device including photonic crystal structures.
2. Description of the Related Art
Laser devices, in general, comprise a material having an optical gain and an optical feedback structure. The optical gain material allows an amplification of a light beam by means of stimulated emission when the optical gain material is brought into a state called population inversion. Stimulated emission is called a process by which an electron, perturbed by an incoming photon may drop to a lower energy level resulting in the creation of a second photon. The perturbing photon is substantially unchanged in the process, and the second photon is created with the same phase, frequency, polarization, and direction of travel as the original. The above process can be thought of as “optical amplification.”
As an optical feedback structure, a distributed feedback structure (DFB) may be used which is made of a dielectric material and employs planar structures on a substrate which the optical gain material is applied on. These distributed feedback structures can act as a laser resonator. Distributed feedback structures are usually provided as photonic crystals and the structures have single structures with a periodicity in at least one plane direction, wherein their dielectric constant is periodic. Usually, the distributed feedback structures provide elevations of a feedback material having a first dielectric constant in between which and above which the optical gain material is provided having a second dielectric constant.
The photonic crystals can be dimensioned to support optical waves of specific wavelengths. If the distributed feedback structure is designed as a two-dimensional photonic crystal, the photonic crystal can be provided for supporting different orders of resonance wavelengths. If designed in second order, light can be coupled out perpendicularly to the extension of the two-dimensional photonic crystal. This is a result of a fan-like emission pattern of two orthogonal directions in which optical feedback is provided. The fan-like emission patterns are superimposed so that an emitted light beam is created by interference of the emission patterns.
The aforementioned second-order distributed feedback structure has losses at the edge of the feedback region, which even increases for smaller devices having a smaller periodicity, i.e. the number of a repetition of the single structures in one plane direction. Since the provision of mirrors to reflect the light at the edges into the second-order distributed feedback structure can be badly integrated as planar structures, the use of first-order feedback structures has been proposed which have no perpendicular emission of light and can therefore be used as mirrors on the edges of the second-order feedback structure. The first-order feedback structures are also called distributed Bragg reflectors (DBR). The first-order feedback structure can be arranged on two opposing edges of the second-order feedback structure or can preferably be arranged surrounding the plane of the second-order structures to provide a reflection on all edges of the plane.
A laser device formed by a distributed feedback structure and an optical gain material can be excited by using an optical pump power directed to the optical gain material, wherein the light output can be switched on and off by increasing or decreasing the pump power. Current optical switches rely on changing the modulation of refractive indices. There, the amount of modulation is proportional to the non-linear susceptibility namely the optical Kerr effect. A drawback of these optical switch devices is that known materials usually show very small non-resonant non-linearities. Hence, devices build from these materials require excessive switching power. A further disadvantage is that devices comprising these materials cannot be easily integrated into high density optical interconnects.
For instance, Nozaki et al., “Resonantly photopumped lasing and its switching behavior in a photonic crystal nanolaser”, Applied Physics Letters 92, 021501 (2008), describes a wavelength switching in a photonic crystal structure including defects by wavelength variations of the pump source. The switching occurs between a dipole and a monopole mode showing different wavelengths.
Document US 2007/0013 991 A1 describes a photonic crystal semiconductor device for wavelength filtering and lasing by means of a photonic crystal structure with defects.
Yu et al., “Fast intra-modal and inter-modal wavelength switching of a high-speed SG-DBR laser photon dynamic wavelength routing”, Optical and Quantum Electronics 33: pages 641 to 652, 2001, Kluwer Academic Publishers, describes inter-modal wavelength switching in a sampled-grating DBR laser.